Total knee replacement (TKR) surgery and component systems for replacing compartments of a knee in total replacement surgery are well-known. Typically, the surgery involves resecting the distal end of a femur so a femoral component may be mounted to the femur. The femoral component replaces the lateral condyle, medial condyle, and patellofemoral portions of the femur because one or more of these areas of the knee are diseased and are no longer wearing well or providing an adequate range of motion for a patient.
In TKR surgery, the proximal end of the tibia is also resected so that a tibial component may be mounted to the tibia to receive the lateral and medial condyles of the femoral component. The tibial component may be comprised of a material having a low coefficient of friction to simulate the meniscus being replaced by the tibial component.
Thus, a TKR system includes components for use in three compartments: the medial tibial femoral compartment, the lateral tibial femoral compartment and the patella femoral compartment, for which the opposing areas of the femur, tibia and patella are prepared for mounting.
U.S. Pat. No. 3,816,855 discloses one such system. The '855 patent discloses a unitary femoral component in the form of a shell with two condylar portions. The outer surface of the shell is formed to conform to the natural shapings of the corresponding parts of the knee joint. The inner surface of the shell mirrors this shape, presenting a surface that is curved in the medial lateral direction as well as the anterior posterior direction. While providing a number of benefits, the device of the '855 patent suffers from several limitations.
The preparation of a subject for TKR surgery usually causes substantial trauma. A large incision is required for insertion of all of the components of a TKR system and the bone resection required for mounting of the components may require extensive recovery time. Thus, single piece replacement components such as the device of the '855 patent require a large incision.
In an effort to reduce this trauma, and accordingly, reduce the recovery time associated with such surgery, TKR systems have been developed that provide TKR components in parts that mate to form the larger TKR components.
U.S. patent application No. US 2003/0158606 discloses such a system of TKR components. As shown in that application, the femoral component may consist of two or three pieces. Each of these pieces is smaller than the femoral component that they form when they are assembled in the knee. As a result, the incision required for insertion of these pieces is smaller than an incision for a femoral component having all of these pieces in a single component. Likewise, the tibial component consists of two parts, each of which is smaller than the tibial component that they form when assembled in the knee.
U.S. patent application No. US2002/0138150 A1 discloses an alternative two-piece femoral component that allows a center part and a condyle part to be pushed onto a femur separately during implantation. The different parts are then joined according to conventional means. The device of the '150 application further describes guides that are intended to aid in tracking of the patella during extreme flexion.
However, both the '606 application and the '150 application use traditional methods of attaching the replacement components to the femur and/or to other components. Such methods are limited by the very nature of minimally invasive surgery. For example, the small incision(s) offers a very limited access to the prosthesis implantation site. Thus, any mechanism used to join the components to other components or to the bone must be accessible from the small incision. This necessarily limits the design of the mechanism. Moreover, it is more difficult to ascertain that two components have been properly connected in situ. This problem is exacerbated for components that are designed to be connected with very small tolerances.
Moreover, even if the components are precisely connected, problems arise as the replacement components are exposed to different stresses and impacts. Such forces tend to create relative movement between the adjacent components which is exacerbated if the components have been improperly connected. The relative movement of the adjacent components causes rubbing of the components generating frictional debris. The frictional debris tends to move with fluid transfer along the interface between the prosthesis and the surrounding soft tissue, and also tends to enter the intramedullary space between the prosthesis stem and the surrounding remaining bone portion. The biological reaction to these small wear particles causes the surrounding bone tissue to be lysed, thereby weakening the bone and potentially causing additional loosening of the prosthesis and subsequent bone failure.
Yet another limitation of implant systems is that as a commercial consideration, many replacement components are mass-produced. While beneficially lowering the cost of implants, these systems are generally provided in a limited number of discrete sizes that most likely will not be precisely the size needed for a patient. For example, a patient's femur may measure 75-mm in diameter. However, available implants for this patient may measure 70-mm and 80-mm. Thus, a surgeon must replace the natural femur with a component that is either too large or too small.
What is needed is a system and method for performing TKR surgery so that wear debris from adjacent pieces of a prosthesis system is reduced.
What is needed is a system and method of implanting femoral components that more closely reflects the size of the natural femur.
What is needed is a system and a method of implanting femoral components that allow the size of the joined components to be individualized.
What is needed is a system and a method of implanting femoral components that provide greater design flexibility in the manner in which adjacent components are connected.